Answers: Weather balloons and airplanes

By Jack Williams ©2015

Q: Hi, I enjoyed “Rise Up” in the March 2010 AOPA Flight Training magazine.   I wonder about  the danger of those weather balloons and noted your  comments about there being “no danger” as it’s floating down under parachute.

But really, hasn’t there ever been an incident or accident associated with one of these balloons where one of them (either going up or down) and an airplane were in the same place at the same time? Does the government have any odds calculated on the possibility? — Warren, Cromwell, Conn.

A: Your question makes me realize that I was a little glib in saying there was “no danger” in my March 2010 Flight Training article.

NWS weather balloon

An NWS weather balloon. The parachute is in the middle with the instrument package, the radiosone, at the bottom. NOAA photo

There is a danger but experience shows it is extremely small.

In answer to my question, Joe Facundo, chief of the National Weather Service’s Observing Systems Branch Chief, e-mailed that, “We don’t have any record of a weather balloon striking an airplane.”

Also, I searched the National Transportation Safety Board’s Accident Database & Synopses for the term “weather balloon.” The database covers all accidents the NTSB has investigated since 1962.

Only a couple of dozen reports included the term “weather balloon” in the text and in all but one of these cases, the term was used to identify the source of weather data investigators used. The one exception involved a collision of two helicopters over Seattle in the 1990s. Both landed safely with no injures. One of the pilots hadn’t realized he had collided with another aircraft. He said he thought he had hit a weather balloon that he hadn’t seen.

Facundo also notes that with the NWS complies “with all FAA regulations. Before launching a balloon from forecast offices near airports, the NWS generally calls the FAA to coordinate each launch.”

In fact, the NWS weather balloons operations manual (available as a PDF file) requires that before launching a balloon within five miles of a controlled airport, the weather observer launching the balloon has to coordinate with the airport’s ATC. Also, at all sites,  “the observer will check the horizon to ensure there are no aircraft or other activity that the balloon might interfere or endanger. If aircraft or other activities are present, the observer will postpone the launch until it is safe to launch,” the manual says.

The instrument packages the balloons carry aloft weigh from approximately half a pound to a little more than a pound. This is well under the six-pound weight for which the Federal Aviation Regulations (FAR part 101) requires that a NOTAM (Notice to Airmen) be issued before the launch of a free balloon.

While the odds of a collision with a weather balloon are small, there is some danger, wrote Mitch Mitchell in the May 1, 2009 issue of IFR magazine.  Writing about the six-pound rule in FAR 101, Mitchell wrote: “The thinking must have been that we could survive a collision with six pounds in flight. But I’m not so sure.”

He also notes that the balloons rise at the rate of approximately 1,000 feet a minute–faster than general aviation airplanes can–and are not easy to see visually or with radar. On the other hand, he notes that the data the twice-daily launches from 92 stations in North America and from U.S. Pacific islands, are vital for weather forecasts that pilots and others need.

As for the question about a calculation of the odds of an aircraft hitting a weather balloon, I could find no one who’s heard of anyone doing this.

Pilots could do one thing to lower the already low odds. If you are planning to take off or land at an airport near where weather balloons are launched, you could be extra careful around the noon and midnight Zulu time regular balloon launches; maybe wait until ATC tells you the balloon has been launched–remember they climb at approximately 1,000 feet a minute.

By the way, balloons are also launched at times other than noon and midnight Zulu when they are needed to collect additional data to predict threatening weather such as tornadoes or an approaching hurricane. But these are times you might not want to be flying.

An easy way to find out where balloons are launched is from the University of Wyoming Atmospheric soundings Web page. You can also obtain the latest or past observations by clicking on a weather station code on the map.

I discuss upper air observations, including with balloons, on pages 136 to 139 of my AMS Weather Book. The NWS Radiosonde Fact Sheet has more information.

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